In the course of the ongoing digitalization of life, a large variety of different categories of battery-powered portable electronic devices have been conceived, of which the ubiquitous smart phone is only the most prominent one. Further categories comprise, for example, media players, portable computers such as tablet computers, hearing aids, and health and fitness monitoring devices to be worn by a user, e.g. a patient. A particular category, which has recently gained a lot of momentum, is typically referred to as “wearable devices” or in short “wearables”. This category comprises, for example, so-called smart watches, fitness tracking devices and other health-related electronic devices, such as health monitoring sensor devices, all of which are designed to be worn by a user, often directly attached to his body. Alternatively, they may for example also be embedded within a piece of clothing, such as a shirt. On the one hand, this allows for providing sensors on the device that are suitable for detecting certain properties or states of the human body, such as the user's current pulse or the humidity of his skin surface. On the other hand, this provides an opportunity to integrate electromechanical actuators within the devices that can silently interact with the user and thus send hidden signals. For example, such an actuator could cause a motion, such as a vibration, that can be sensed by the user wearing the device on his body, e.g. at his wrist, while the motion and any related sounds are difficult or even impossible to be sensed by others. The so-called “tactile engine”, used in the Apple Watch® sold by Apple Inc. of Cupertino, is a well-known example of such an actuator. It can, for example, be used to signal an upcoming calendar event to the user by causing a short tapping motion which the user can sense. For the category of cell-phones, the use of electromechanical actuators as vibration alarms has been known for a long time. Loudspeakers comprising an inductor, often referred to as “voice coil”, are other examples of electromechanical actuators that are typically used in portable electronic devices. Sometimes, a loud-speaker may even be operated in a particular “overdrive” mode as a vibration device using the voice coil as a moving mass.
For many typical applications, battery-powered portable electronic devices, in particular wearables, feature a stylish design and need to be reasonably rugged and weather-sealed for their intended purpose. For example, it is desirable that smart watches and fitness trackers be sealed and waterproof and thus allow for being used while swimming or diving or in other harsh environments, where the device might get exposed to liquids, materials or even gases, which could potentially cause a malfunction of the device or even damage it, if they were able to penetrate into its interior. Therefore, moving away from using open-plug-type connectors for connecting the portable devices via an electric wire to a power supply, using wireless charging instead has become a recent trend. However, most portable electronic devices have to meet a small form factor as an additional requirement, which poses a significant challenge to the integration of a wireless charging capability requiring additional components. Furthermore, the efficiency of wireless charging may be limited by shielding effects of magnetic materials within the portable device, such as certain metal parts or even permanent magnets.
US 2014/0241555 A1 discloses an electronic device comprising an input-output device such as a speaker, a vibrator, or a near field communications antenna, wherein the input-output device may include an inductor. The inductor in the input-output device may be shared by a wireless charging circuitry in the electronic device so that wireless charging signals can be converted into power to charge a battery in the electronic device. A drive circuit may supply drive signals to the input-output device such as audio signals, vibrator control signals, or near field communications output signals for external near field communications equipment.